Examples of traditional flat light sources include light emitting diodes (LEDs) provided with light guiding plates, and organic light emitting diodes (OLEDs) or organic electroluminescent devices (OLEDs).
Smart devices, such as smart phones and tablets, have gotten exponential increased sales on a world scale from around 2008. These smart devices are provided with a keyboard having a flat face in view of user-friendliness. For example, the keyboard corresponds to the icon region including common functional key buttons provided at the bottom of a smart device. One example combination of the common functional key buttons consists, for example, of “Home” (indicated by a square mark), “Return” (indicated by an arrow mark), and “Search” (indicated by a loupe mark).
In order to improve the visibility of these common functional key buttons, for example, LEDs are disposed together with a flat emission device, such as an LED light guiding plate, in tune with the pattern of the mark to be displayed in the interior of the smart device, as is disclosed, for example, Patent Literature 1.
A capacitance-type information input unit with an LED light source is also disclosed. This input unit includes a flexible printed circuit (FPC) having a highly sensitive sensor electrode that can certainly detect a variation in electrostatic capacitance and stabilize the input operation by a user, and an adhesive layer having a dielectric constant higher than that of an air layer having the same shape and disposed at positions other than the icon regions between the circuit and a surface panel (refer to, for example, Patent Literature 2).
Besides the LED light sources, use of surface emitting organic electroluminescent devices has come into action for display of icon regions for the purpose of a reduction of electric power consumption and more uniform light emission brilliance in recent years. To achieve display functions, these organic electroluminescent devices are provided on the rear sides of cover glasses, while icon marks have been preliminarily printed on the front sides of the cover glasses.
Smart devices inevitably require touch functions for use, and capacitive touch sensing devices for from display portions to common functional keys are usually disposed on the rear sides of the cover glasses.
A typical touch sensing device includes a film/film-type touch sensor that is enlarged to the size of a cover glass and is laminated to the cover glass. For devices that can have any thickness, a touch sensor of a glass/glass type is also used in some cases. An electrostatic capacitance scheme has been applied to touch detection in many cases in recent years. “Projective capacitive touch sensors”, which have fine electrode patterns along the x and y axes, have been used in main displays. In this scheme, two or more points can be touch-detected (so called “multi-touch”).
Since such a touch sensor is used, a light emitting device having no touch function has been used at a common functional key portion. Displays of an “in-cell” or “on-cell” type placed on the market, however, have highly demanded light emitting devices having dedicated touch sensing functions for common functional keys.
In a surface emission organic electroluminescent device, an anode, a cathode, or a metal foil protective layer adversely affects the detection of the capacitance in the surface capacitive scheme; hence, for an organic electroluminescent device having electrostatic touch functions, an independent touch sensing electrode as an assembly should be provided for detecting a touch composed of an electrical connecting unit on a flexible board provided with an electrostatic detecting circuit and a wiring portion, for example, a flexible print circuit (FPC), together with an organic electroluminescent panel, adjacent to the light emitting side, as shown in FIG. 1 (described later) Such a structure inevitably has a large thickness due to increased components and thus its use is restricted. In use of such an assembly, a device for detecting the touch, such as an FPC, should be additionally prepared, resulting in several disadvantages, such as increased costs, increased thicknesses of the devices, and increased production steps.
Development of a thin compact organic electroluminescent module suitable for smart devices is highly demanded in which organic electroluminescent devices for icon regions and wiring material for controlling the drive of the devices are effectively disposed.